Magnetoresistance Values Research Articles

Effect of Mn-site doping on the magnetofunctional behaviors of Mn5Si3 alloy

Present work reports a detailed investigation on the magnetoresistance and magnetocaloric behavior of Ni and Cr-doped Mn5Si3 alloys with general formula Mn5−xAxSi3 (where A = Ni/Cr; x = 0, 0.05, 0.1 and 0.2). Both pure (undoped) and doped alloys show a reasonably large amount of magnetoresistance (MR). Doping at Mn-site, both by Ni and Cr, results in a monotonic decrease in MR values. Magnetocaloric effect (MCE), on the other hand, is found to be interesting, and all the alloys show both conventional and inverse MCE around the magneto-structural transition temperature. Among the two types of MCE observed, the inverse MCE is found to decrease with increasing doping concentration and consistent with the MR behavior, whereas doping results in a significant increase in conventional MCE values.

Electrical and magnetic properties of La0.7Ca0.3MnO3 nanoparticle prepared by reactive milling method

La0.7Ca0.3MnO3 nanoparticle in an orthorhombic structure with space group of Pnma was prepared by a combination of the reactive milling method and annealing at 900 °C for 1 h in air. The mean crystal size determined through the powder x-ray diffraction data is 18 ± 2 nm. Based on the dependences of the resistivity and the magnetisation on temperature and applied magnetic field, the electrical-magnetic properties, the magnetoresistance and the magnetocaloric effects have been investigated. It shows La0.7Ca0.3MnO3 nanoparticle undergoes a metal-insulator and a ferromagnetic-paramagnetic phase transitions at T MI = 252 K and T C = 253 K, respectively. The temperature dependences of resistivity of material in the absence and presence of 4 kOe in a range of 30–300 K were fitted to the phase segregation model. The magnetoresistance and the magnetocaloric effects related to the double-exchange interactions taking place around T MI and T C were observed, corresponding to the values of the magnetoresistance MR = 9.29% and the maximum magnetic entropy change ∣ΔS max∣ = 0.18 J/kg.K under an applied magnetic field of 4 kOe. Besides, the low field magnetoresistance value at low temperature region and the change of the specific heat of La0.7Ca0.3MnO3 nanoparticle have also been concerned.

Influence of composition on the structural-phase state, electrophysical and magnetotransport properties of alloy thin films based on Co and Cu

The influence of the composition of alloy thin films based on Co and Cu on their structural-phase state, electrophysical and magnetotransport properties is presented. The studies were performed for non-annealed and annealed (up to Tmax = 800 K) alloy thin films based on Co and Cu with a thickness of 40 nm, in a wide range of cobalt atomic fractions (0.20 ≤ x ≤ 0.75). For alloy thin films with x ≤ 0.42, thermal treatment in the temperature range from 300 to 800 K for 30 min caused an increase in the value of the giant magnetoresistance (GMR) and coercivity due to the increase in the size of the hcp-Co granules. The highest amplitude of GMR were found in alloys thin films with a total atomic fraction of Co at x = 0.32. The calculation of the thermal coefficient of resistance of alloys showed a qualitative agreement with experiment results for alloy thin films with a total atomic fraction Co x ≤ 0.32.

Metallic (CoFe)/Cu superlattices with record microwave giant magnetoresistive effect

Technology of preparation of (CoFe)/Cu superlattices by magnetron sputtering is discussed. The parameters of growth have been obtained which allows to get superlattices with very high magnetoresistance. Methods of characterization of superlattices are described. Microwave magnetoresistance in millimeter waveband is measured by transmission method. The record value of microwave magnetoresistance exceeding 80% is obtained.

Room Temperature Synthesis of Colossal Magneto-Resistance of La2/3Ca1/3MnO3: Ag0.10 Composite

Rare-earth manganite-based perovskite has great potential as a promising material for spintronics and ferroelectromagnets. Herein, we have synthesized La2/3Ca1/3MnO3:Silverx (LCMO-Agx; where x = 0.00 and 0.10) composite using a standard solid-state reaction route. Their structural and physical properties have been investigated. Pristine LCMO and LCMO-Ag composite are crystallized in an orthorhombic structure, which is in a single-phase and has a space group of Pbnm. Pristine LCMO and LCMO-Ag composite’s structural analysis showed better grain connectivity in ferromagnetic domains of LCMO-Ag composite compared to pristine LCMO. Ag doping enhances the paramagnetic-ferromagnetic transition Tc (Curie temperature) to 277 K, which is 8 K higher than that of pristine LCMO (Tc = 269 K). Additionally, the magneto-resistance (MR) of LCMO-Ag composite was improved by ∼10% with Ag doping even at room temperature (RT), which is due to improved connectivity and grain size with Ag doping. Thus, the enhanced value of MR at RT may efficiently open up the possible use of LCMO-Ag composite as ferroelectromagnets and spintronics applications. Additionally, LCMO thin films can be useful in artificial planar junctions, vertical tunnel junctions, and sensing applications.

Large spin-dependent tunneling magnetoresistance in Fe3O4/PET heterostructures developed at room temperature: A promising candidate for flexible and wearable spintronics

Half-metallic nanocrystalline magnetite (Fe3O4) thin films, with different thicknesses were developed on polyethylene-terephthalate (PET) substrates, by reactive sputtering at room temperature. Fe3O4 film (200-nm thick)/PET heterostructures possess superior electrical and magnetic characteristics, with a Verwey transition temperature (Tv) of ~122 K and a saturation magnetization (Ms) ~ 361 emu/cm3. Furthermore, the antiferromagnetic (AFM)-coupled antiphase boundaries (APBs) controlled the transport properties of the Fe3O4 thin films, due to the tunneling of spin-polarized electrons through the films. Very-high magnetoresistance (MR) value (−8.9%) were observed for H‖Film plane, constructed from Fe3O4 (200-nm thick)/PET when H values were below 60 kOe at 300 K. In addition, flexibility tests, to examine resistivity, M-H and MR, were performed using with 90° and 45° bent angles and cyclability experiments were implemented to validate the reproducibility of these characteristics. These outcomes demonstrated that Fe3O4/PET heterostructures may represent a promising candidate for flexible/wearable spintronics.

Effects of transitional hysteresis on the large magnetocaloric and magnetoresistance properties of Ni-Mn-Co-Sn Heusler alloy

Ni-Mn-Co-Sn based Heusler alloys have drawn immense attention lately due to their significant magnetocaloric (MC) and magnetoresistance (MR) properties near their first-order magneto-structural martensite transformation (MT). Here, we have studied the influence of thermal and magnetic hysteretic behaviours in the temperature and field dependent magnetization and resistivity in Ni45Mn39Co5Sn11 bulk Heusler alloy across the MT regime. This is critical since hysteresis losses could significantly compromise the MC and MR properties in these compounds in practical applications. Isothermal X-ray diffraction measurements at different temperatures reveal that the MT temperature is near room temperature in Ni45Mn39Co5Sn11 alloy. Thermodynamic analyses of isothermal field dependent magnetization data result in large isothermal magnetic entropy changes (ΔS = 17–18 J kg−1 K−1) under a field change (ΔH = 8 T) at 364 K across the MT regime. The calculated refrigeration capacity values (RC = 173–179 J kg−1) for decreasing and increasing fields are significant and independent of magnetic hysteresis across the MT regime. A large adiabatic temperature change (│ΔT│ = 10.4 K for ΔH = 8 T at 364 K) is being reported in Ni45Mn39Co5Sn11 Heusler alloy, which makes it promising for MC applications. Further, the influence of martensite-austenite phase fractions on the MC and MR properties in Ni45Mn39Co5Sn11 alloy has been studied across the MT regime using isofield and isothermal magnetic and magneto-transport measurements. A strong correlation has been established between the observed MR (−36.8%) and the transformed austenite phase fraction using both experimental data and theoretical model. The large RC, │ΔT│, MR values close to the room temperature and the role played by the thermal and magnetic hystereses on the MC and MR properties make the Ni45Mn39Co5Sn11 Heusler alloy an interesting material for technological applications in magnetic refrigeration and switching devices.

Critical behavior and magnetocaloric effect in Co-doped nanocrystalline La0.7Te0.3Mn1-xCoxO3

We have explored the impact of cobalt doping on magnetic, magnetocaloric and electrical transport properties of the nanocrystalline La0.7Te0.3Mn1-xCoxO3 (0.1 ≤ x ≤ 0.5) samples synthesized using sol-gel method. The Rietveld refinement of the X-ray diffraction (XRD) patterns confirmed the rhombohedral crystal structure for x ≤ 0.2 samples and orthorhombic crystal structure for x ≥ 0.3 samples. The temperature dependence magnetization data proposed that each sample experienced a transition in phase from paramagnetic to ferromagnetic. The maximum values of magnetic entropy change |ΔSMmax| were calculated to be 2.93 Jkg−1K−1, 2.62 Jkg−1K−1, 2.04 Jkg−1K−1, and 1.71 Jkg−1K−1 for ΔH = 5 T respectively for x = 0.1, 0.2, 0.4, and 0.5 samples. Detailed critical exponent analysis was done for each sample and the nature of magnetic phase transition for x = 0.1 follows the 3D Heisenberg model, while for x = 0.2 and 0.3 pursue the mean field model. For x = 0.4 and 0.5, none of the models describe completely the magnetic phase transition. The temperature-dependent electrical resistivity ρ(T) data exhibit semi-conducting like behavior within the studied temperature range for x = 0.1 and 0.2 compositions. The magnetoresistance (MR %) values for x = 0.1 and x = 0.2 respectively were 44%, and 35% at a field change of 5 T around their respective transition temperatures. Relatively high values of |ΔSMmax| and MR% made the studied samples suitable for multifunctional device applications.

Spin transport through metal-dichalcogenides layers: a study from first-principles calculations

Spin transport through monolayer and trilayers of molybdenum dichalcogenides were studied considering Co as leads. Detailed investigations of the electronic structure of the Co/MoS2 interface and magnetic tri-junctions are carried out by using density functional theory calculations to understand transport behavior. The study revealed that new spin-polarized hybridized states appeared at the Fermi level due to the formation of Co/MoS2 interface that effectively acted as a spin filter and enhanced the spin injection efficiency of the systems. Spin-polarized current through the system as well as the magnetoresistance (MR) was estimated at different applied bias voltages. Large MR up to 78% was calculated for the trilayer MoS2 system at a relatively high applied bias voltage. The MR values are further improved by tuning the structure of the scattering region. A very large MR of 123% for MoS2/MoSe2/MoS2 trilayer at an applied bias 0.8 V was observed, which is much higher than the previously reported bias dependent MR values in similar systems.

Concentration and heat treatment effects on magnetoresistive properties of three-layer film systems based on FexСо100-x and Cu

The magnetoresistive properties of FexCo100-x/Cu/FexCo100-x/S three-layer films (x ≅ 0-100 at.%) with the thickness of feromagnetic dF = 15-30 nm and non-magnetic dN= 3-15 nm layers were researched. The deposited films were annealed at temperatures of 400, 550, and 700 K for 15 min. It demonstrated the presence of negative magnetoresistance for as-deposited and annealed at 400 and 550 K thin films. The maximum value of the isotropic magnetoresistance at room temperature is 3-4% for FeхСо100-x/Cu/FeхСо100-x/S (x ≅ 0-10 at.%) thermally stabilized at 550 K films with dF = 30 nm and dN = 5 nm. The heat treatment of samples at 700 K leads only to the decrease of isotropic magnetoresistance.

XAS and XPS analysis of double magnetic transition, canonical spin glass behavior and magnetoresistance in LaMn1-xCoxO3 (0.1 ≤ x ≤ 0.5) system

Polycrystalline LaMn1-xCoxO3 (0.1≤ x ≤ 0.5) samples were synthesized using conventional ceramic method. Rietveld refined X-ray diffraction pattern revealed the single-phase orthorhombic crystal structure of all the samples with the space group Pbnm. Temperature-dependent magnetic measurements performed in field cooled (FC) and zero field cooled (ZFC) mode at 102 Oe exhibit the onset of double transition in x = 0.3–0.5 compositions. The ordering temperature rises with an increase in Co concentration. FC and ZFC studies show the presence of glassy state below the ordering temperature in all samples; confirmed using a. c. susceptibility measurements. The a. c. susceptibility data are analyzed using power law and the existence of canonical spin glass is revealed. Magnetic hysteresis studies demonstrate the enhanced ferromagnetism amid the presence of unsaturated magnetization with an increase in Co doping. The presence of double transition and spin glass state is attributed to the competing ferromagnetic and anti-ferromagnetic interactions between the Co and Mn ions present in the system. The system also depicts the presence of appreciable value of magnetoresistance ~42% at 8 T magnetic field in x = 0.5 sample. These properties are interpreted through valence and spin states of Mn and Co ions, being confirmed from electronic structure studies using X-ray absorption spectroscopy (XAS) at L3,2- edges of respective ions along with O K-edge for all samples (0.1≤ x ≤ 0.5). After meticulous analysis and conjoining the results obtained from magnetization and XAS studies, it is found that cobalt is present in high spin Co2+ and high/low spin Co3+-state. Charge transfer multiplet calculation done at L3,2 edges of Mn and Co ions confirm the presence of Mn3+/Mn4+ and Co2+/Co3+ states consistent with XAS results. X-ray photoelectron spectroscopy performed at Mn2p, Co2p, and O1s -edges further substantiate the reasons behind the properties exhibited by the present system.

Anomalous Hall effect and negative longitudinal magnetoresistance in half-Heusler topological semimetal candidates TbPtBi and HoPtBi

Half-Heusler compounds have attracted significant attention because of their topologically non-trivial electronic structure, which leads to unusual electron transport properties. We thoroughly investigated the magnetotransport properties of high-quality single crystals of two half-Heusler phases, TbPtBi and HoPtBi, in pursuit of the characteristic features of topologically non-trivial electronic states. Both studied compounds are characterized by the giant values of transverse magnetoresistance with no sign of saturation in a magnetic field up to 14 T. HoPtBi demonstrates the Shubnikov–de Haas effect with two principal frequencies, indicating a complex Fermi surface; the extracted values of carrier effective masses are rather small, 0.18 me and 0.27 me. The investigated compounds exhibit negative longitudinal magnetoresistance and anomalous Hall effect, which likely arise from a nonzero Berry curvature. Both compounds show strongly anisotropic magnetoresistance that in HoPtBi exhibits a butterfly-like behavior.

Magneto-transport and electronic structures in MoSi2 bulks and thin films with different orientations

We report a comprehensive study of magneto-transport properties in MoSi2 bulk and thin films. Textured MoSi2 thin films of around 70 nm were deposited on silicon substrates with different orientations. Giant magnetoresistance of 1000% was observed in sintered bulk samples while MoSi2 single crystals exhibit a magnetoresistance (MR) value of 800% at low temperatures. At the low temperatures, the MR of the textured thin films show weak anti-localization behaviour owing to the spin orbit coupling effects. Our first principle calculation show the presence of surface states in this material. The resistivity of all the MoSi2 thin films is significantly low and nearly independent of the temperature, which is important for electronic devices.

High-sensitivity tunneling magneto-resistive micro-gyroscope with immunity to external magnetic interference

Micro-electro-mechanical system (MEMS) gyroscopes have numerous potential applications including guidance, robotics, tactical-grade navigation, and automotive applications fields. The methods with ability of the weak Coriolis force detection are critical for MEMS gyroscopes. In this paper, we presented a design of MEMS gyroscope based on the tunneling magneto-resistance effect with higher detection sensitivity. Of all these designed parameters, the structural, magnetic field, and magneto-resistance sensitivity values reach to 21.6 nm/°/s, 0.0023 Oe/nm, and 29.5 mV/Oe, thus, with total sensitivity of 1.47 mV/°/s. Multi-bridge circuit method is employed to suppress external magnetic interference and avoid the integration error of the TMR devices effectively. The proposed tunneling magneto-resistive micro-gyroscope shows a possibility to make an inertial grade MEMS gyroscope in the future.

Giant Magnetoresistance and Magnetocaloric Effect in Highly Textured Ni45Mn36.5In13.5Co5 Alloys

Herein, the giant magnetoresistance (MR) and magnetocaloric effect (MCE) of highly textured Ni45Mn36.5In13.5Co5 alloys are investigated. The Ni45Mn36.5In13.5Co5 alloys are grown using the liquid‐metal‐cooling directional solidification technique. In the scanning electron microscopy (SEM) image, unique bamboo‐like transverse stripes perpendicular to the long axis of grains are observed, which may lead to the giant MR of the sample. For the magnetic field change of 10 kOe, the giant MR value at 268 K is ≈−64%, which is rather big among similar bulk alloys. The MCE is evaluated via the magnetic entropy change. In H⊥ and H∥ magnetic fields of 30 kOe, the maximum entropy change is 13.5 and 15.3 J kg−1 K−1, and the effective refrigeration capacity (RC) reaches ≈108 and ≈117 J kg−1. The detailed results indicate that the MCE properties of the studied alloys vary in different directions under a low magnetic field; however, the difference is not very significant under a high magnetic field.

Size Effects on Charge Transport Mechanisms and Magnetotransport Properties of Pr0.67Sr0.33MnO3 Nanoparticles

This paper covers a detailed study of the sintering temperature (TS) effect on the electrical and magnetotransport properties of Pr0.67Sr0.33MnO3 nanoparticles prepared by sol–gel method. The temperature dependence of resistivity displays a metal–insulator transition with increasing temperature. The electrical resistivity is strongly affected by particle size. The resistivity minimum at low temperature is associated to electron–electron coulombic interactions. Magnetotransport analysis was carried out using a phenomenological percolation model for all our samples. The obtained results indicate that a percolation model is not suitable for samples presenting high magnetic disorder. The magnetoresistance (MR) can be modulated by particle size effect. We have recorded considerable MR values (−MR(T) = 34% at 10 K for a 1T field when TS = 850°C, −MR(T) = 33% at 290 K for a 2T field when TS = 1000°C and −MR(H) = 33% at 5 K for a 1T field when TS = 700°C). The considerable MR values indicate the possibility of using these samples for several technological applications.

Magnetoresistance, magnetothermopower, magnetothermal conductivity and magnetostriction in La1-xNaxMnO3[formula omitted

We report the influence of the magnetic field on electrical resistivity (ρ), thermal conductivity (κ), thermopower (S), and linear thermal expansion (ΔL/L0) in La1-xNaxMnO3 series (x = 0, 0.01, 0.02, and 0.05) over a wide range of temperature. While LaMnO3 is an antiferromagnetic insulator, the doping with Na weakens the inter-planner antiferromagnetic coupling and transforms it into a ferromagnetic metal by promoting the double exchange coupling between Mn3+ and Mn4+ ions. ρ and S show peaks, whereas, κ shows a sudden increase at the onset of ferromagnetic spin ordering in the samples. Dominant charge carriers are holes in these doped compounds as indicated by the positive sign of S. High-temperature transport is explained in the context of the small polaron hopping model. External magnetic field influences thermal properties (S and κ), and ΔL/L0 mostly around the Curie temperature (TC), while it affects ρ to as low as 10 K. Enhancement of κ at the insulator-metal transition, on the application of external magnetic field, suggests a decrease in spin-wave scattering. The highest value of negative magnetoresistance (~69.7%) and negative magnetothermopower (~80.4%) is obtained for x = 0.02 and the value decreases for higher dopant concentration.

Impact of Fe80B20 insertion on the properties of dual-MgO perpendicular magnetic tunnel junctions

We explore the impact of Fe80B20 inserted at both Co20Fe60B20/MgO interfaces of dual-MgO free layers (FLs) in bottom-pinned magnetic tunnel junctions (MTJs). MTJ stacks are annealed for 30 min at 350 °C and 400 °C in a vacuum after film deposition. Current-in-plane tunneling measurements are carried out to characterize magnetotransport properties of the MTJs. Conventional magnetometry measurements and ferromagnetic resonance (FMR) are conducted to estimate the saturation magnetization, the effective perpendicular anisotropy field and the Gilbert damping of dual-MgO FLs as a function of the Fe80B20 thickness and annealing temperatures. With ultrathin Fe80B20 (0.2–0.4 nm) inserted, perpendicular magnetic anisotropy (PMA) of FLs increases with similar tunnel magneto-resistance (TMR) and low damping values. As Fe80B20 layer thickness further increases (0.6–1.2 nm), both TMR and PMA degrade, and damping increases dramatically. This study demonstrates a novel approach to tune properties of MTJ stacks with dual-MgO FLs up to 400 °C annealing, which enables MTJ stacks for various applications.

Thickness- and substrate-dependent magnetotransport properties of lanthanum–strontium manganite films with overstoichiometric manganese content

Electrical and magnetoresistive properties of the La0.6Sr0.2Mn1.2O3±δ (LSMO) films deposited on SrTiO3 single-crystalline and Al2O3 polycrystalline substrates by magnetron sputtering have been studied. The aim of the study is to understand the effect of substrate type on the thickness-dependent evolution of magnetotransport properties of the films of lanthanum–strontium manganites with overstoichiometric manganese content. It is shown that the decrease in the LSMO film thickness below 1000 nm causes the reduction of Curie temperature (TC) and magnetoresistance value at 300 K concomitant with the increase in electrical resistivity. At the same time, the dependence of electrical and magnetoresistance parameters on the substrate structure and type becomes stronger. It is found that TC of LSMOSTO films exceeds and resistivity is smaller than the respective parameters of LSMOAO films, and the difference grows with the decrease in the film thickness. All the results show that the behavior of the doped manganite films with overstoichiometric manganese content differs from that characteristic of stoichiometric in manganese films. These observations can be attributed to the effect of manganese excess on the film growth mechanism, making it different from the manganite films of other compositions.

Magnetite thin films grown on different flexible polymer substrates at room temperature: Role of antiphase boundaries in electrical and magnetic properties

Currently, there is an enormous need for flexible electronic devices given their astonishing competencies. In this view, we investigated the structural, electrical, and magnetic characterstics of magnetite (Fe3O4) thin films with a thickness of 100 nm prepared using a reactive RF sputtering technique at 300 K on polycarbonate (PC), polymethyl methacrylate (PMMA), and polythene terephthalate (PET) flexible substrates. The structural properties showed that the films grown on PC, PMMA, and PET substrates exhibited the pure form of Fe3O4 nanostructures by flowing oxygen with a flow rate of 3.5 sccm. The Verwey transition temperatures (Tv) of ∼123 K, ∼124 K, and ∼126 K; saturation magnetization (Ms) values of ∼220 emu/cm3, ∼235 emu/cm3, and ∼261 emu/cm3; and magnetoresistance (MR) values of −7.1%, −7.3%, and −7.8% under the H∥Film plane below 60 kOe at 300 K for 100-nm-thick Fe3O4 film on PC, PMMA, and PET substrates respectively were observed. These remarkable results were interpreted and the effect of antiferromagnetically (AFM) coupled antiphase boundaries (APBs) was explained, which suggested that Fe3O4/PET heterostructure can be a most promising component for flexible spintronics.